There has been a trend over the past several years to provide agricultural combines of greater threshing capacity. While the size of combines has been increased over earlier designs, there is a practical limit to physical increases in header size.
The productivity of large capacity combines may be increased by operating at a higher ground speed, which requires a higher cutter speed. In the case of a reciprocating sickle type cutter, the inertia related forces in the cutter mechanism increases with the square of the frequency of reciprocation. The present invention is directed to providing a cutting mechanism which operates at high speed without imposing unduly high forces on its drive mechanism. This is achieved by provision of a spring coupled cutting mechanism whose resonant frequency is within the reciprocating frequency range at which the sickle is normally operated for crop cutting purposes. Operating the spring coupled sickle bar, at its drive near resonant frequency, results in a greatly reduced input torque requirement, thus conserving power and energy. Also, the lower forces are expected to result in longer operating life of drive components. It is a more specific object of the invention to provide a wobble drive and torsion bar assembly in a sickle drive which operates near its resonant frequency when the sickle bar is reciprocated at its desired crop cutting frequency.
Heretofore others have suggested the use of wobble drive mechanisms for reciprocating the cutter bar of a mowing device, as shown and described in U.S. Pat. Nos. 3,397,584; 3,444,676 and 3,463,018. Also, heretofore others have suggested the use of resilient spring devices for storing and releasing energy during reciprocation of a sickle bar. Several such arrangements are shown in U.S. Pat. Nos. 14,046; 280,901; 280,902 and 1,078,101.